A. Field of the Invention
The invention relates to a device and a method for measuring dynamic torsional characteristics of a damper assembly that includes a damper unit operably disposed between input and output rotary members.
B. Description of the Background Art
In the prior art, measurement of torsion characteristics of a damper assembly has been performed to obtain static torsion characteristics of the damper assembly by applying torsional vibrations while the damper assembly is maintained in a stationary state. However, the damper assembly is typically used in an automotive vehicle and rotates during operation receiving torsional vibrations in a high frequency range of tens of hertz or more. In view of the above, rotational torsion measuring devices are increasingly being employed for measuring the dynamic torsional characteristics of damper assemblies under conditions close to the actual service conditions.
Description is now given of a manner of measuring dynamic torsional characteristics of a damper assembly by a rotational torsion measuring device with reference to FIG. 6, where the damper assembly is statically retained.
A damper assembly 100 includes an input rotary member 101, an output rotary member 102 and a damper unit 103. The damper assembly 100 is fixed to first and second fixing portions 111 and 112 in a rotational torsion measuring device. More specifically, the input rotary member 101 is fixed to the first fixing portion 111, and the output rotary member 102 is fixed to the second fixing portion 112. The input rotary member 101 is fixed to the first fixing portion 111 via a shaft 113. After setting the damper assembly 100 in the rotational torsion measuring device as shown in FIG. 6, a vibrating (or fluctuating) torque, i.e., a torque for causing vibrations, is applied to the input rotary member 101 via the first fixing portion 111, and a torque Ts and a torsion angle .theta.s are measured, as shown in FIG. 7.
According to the above rotational torsion measuring device, the torque Ts and torsion angle .theta.s are measured within the measuring device as shown in FIG. 6. Therefore, the determined torsion characteristics include characteristics of the measuring device itself. A sensor cannot be attached directly to the damper assembly 100 in the above described configuration. Therefore, the torque Ts of the shaft 113 is measured by a sensor such as a strain gauge, and the torsion angle .theta.s is determined by measuring the angular displacement between the first and second fixing portions 111 and 112. These measured values of the torque Ts and torsion angle .theta.s do not provide complete or accurate indications of the actual damper torsion torque and damper torsion angle of the damper assembly 100 for many reasons, such as the reasons set forth below.
First, the torsion angle .theta.s is a measurement of the difference in angular displacement between the first and second fixing portions 111 and 112. This measurement includes possible rotary displacement of elements other than the input and output rotary members 101 and 102. Further, the measured angular displacement includes displacement attributable to torque which results from inertia of the input rotary member 101 acting on the first fixing portion 111 that is measurable at the location of the sensor measuring the torque Ts. Therefore, the actual damper torsion torque of the damper assembly 100 may be smaller that the torque being measured. Accordingly, the torque applied to the input rotary member 101 increases in accordance with the inertia of the input rotary member 101 and increases variable angular acceleration thereof. Therefore, the torque Ts measured by the rotational torsion measuring device shown in FIG. 6 is smaller than the actual damper torsion torque of the damper assembly 100.
Since the conventional rotational torsion measuring device internally measures the torque and torsion angle as described above, the device cannot determine the torsion characteristics of the damper assembly itself, but can determine only the torsion characteristics containing vibration characteristics of the measuring device. In particular, when the vibrating inertia is large, the shaft has a low rigidity and/or the frequency of the vibrating torque is high, these facts significantly affect the result of measurement.